1. Field of the Invention
The invention relates to a magneto-optical recording medium and a method of reading data from the magneto-optical recording medium, and more particularly, to a magneto-optical recording medium and method of reading data from the magneto-optical recording medium which comprises a guide groove portion having land and groove areas.
2. Brief Description of Related Prior Art
A first conventional magneto-optical recording medium comprises a guide groove portion having land and groove areas.
A first conventional magneto-optical recording and reading method records data in only the land area.
A second conventional magneto-optical recording and reading method is disclosed in Volume 1316 (1990) of the Society of Photo Optical Instrumentation Engineers, Page 35 (Proc. SPIE 1316 (1990) 35). The second conventional magneto-optical recording and reading method records data in both the land and groove areas. The second conventional magneto-optical recording and reading method uses a second conventional magneto-optical recording medium.
The conventional magneto-optical recording medium comprises a plastic substrate , a silicon nitride rough layer, a recording layer of TbFeCo, a silicon nitride interference layer, and a reflection layer of Al.
The plastic substrate has a track pitch Pt of 1.2 .mu.m. The silicon nitride rough layer overlies the plastic substrate and has a thickness of 59 nm. The recording layer overlies the silicon nitride rough layer and has a thickness of 20 nm. The silicon nitride interference layer overlies the recording layer and has a thickness of 114 nm. The reflection layer overlies the silicon nitride interference layer and has a thickness of 40 nm.
The magneto-optical recording medium comprises a guide groove portion having a land area, a groove area, and a boundary area between the land area and the groove area. A level difference between the land area and the groove area is about 80 nm. The boundary area has an inclination angle of about 20 degrees.
When a write laser beam is projected onto a part of the magneto-optical recording medium when the part is objected to a magnetic field having a magnetic field direction for magnetization, a datum is recorded or written in the part of the magneto-optical recording medium. When a read laser beam is projected onto the part of the magneto-optical recording medium, the datum in the part is read by detecting a plane of vibration of a reflected beam of the read laser beam.
In the method of reading data from the magneto-optical recording medium, a polarization direction of a linearly polarized beam of the read laser beam forms an angle with the guide groove portion. The angle is 90 degrees or 180 degrees.
By a method of writing to and reading data from the magneto-optical recording medium, the data are written with a linear velocity of 9.4 m/s in both the land area and groove area of the magneto-optical recording medium, and the data are read from both the land area and groove area of the magneto-optical recording medium. In this case, the method uses a laser beam which has a wavelength of 680 nm. As a result, characteristic curves are obtained. The characteristic curves represent relationship of carrier/noise (C/N) to frequency of the laser beam.
However, in this method, output of reading the data of the land area 18 is not equal to output of reading the data of the groove area. Also, when the polarization direction of the linearly polarized beam of the read laser beam forms the angle with the guide groove portion that is 90 degrees or 180 degrees, the value of the C/N of the land area is not equal to the value of the C/N of the groove area.
Thus, the outputs of reading the data of the land area and the groove area are different, and the values of C/N of the land area and the groove area are different. Therefore, in this conventional magneto-optical recording medium and method of reading the data from the magneto-optical recording medium, it is impossible to reliably read the data of the magneto-optical recording medium.